Events on Thursday, November 29th, 2012

Speaker: Christopher Williams, Kavli Institute for Cosmological Physics, The University of Chicago

Abstract: I will present the design and implementation of the Microwave Detection of Air Showers (MIDAS) experiment, a pathfinder for detection of Extensive Air Showers (EAS) induced by Ultra High Energy Cosmic Rays (UHECRs). The MIDAS experiment uses a multi-pixel imaging telescope instrumented with commercially sourced GHz receivers and custom fast-detection electronics to search for EAS. The microwave detection technique is analogous to the already successful fluorescence technique, but with nearly 100% duty cycle. If successful, the microwave technique will provide an attractive method for instrumenting the extremely large areas required by future UHECR observatories. The first science phase of the MIDAS experiment gathered 61 days of livetime data operating on the University of Chicago campus. I will present the current limits on EAS microwave emission from this data set. The second science phase is underway with installation of the MIDAS detector at the Pierre Auger Observatory in MalargA1/4e, Argentina. Operating in coincidence with the Auger surface detector will greatly increase the sensitivity of the MIDAS experiment.

Abstract: Foreground absorption features in the spectra of distant quasars provide largely unbiased probes of the baryon content of galaxies and the intergalactic medium to high redshift. Absorption features from singly-ionized magnesium (Mg II) are particularly prolific in optical spectra within the range 0.3 < z < 2.0, and are expected to trace a wide range of galaxy environments and halo-disk processes, though detecting the individual host galaxies of these absorbers presents an observational challenge. The extraction of ~100,000 quasar absorption line systems from the Sloan Digital Sky Survey -I/II and -III has begun to revolutionize our understanding of the host galaxies and environments of Mg II absorbers. I will present highlights from my work examining the statistical properties of Mg II host galaxies from stacking and clustering measurements using the largest absorption line data set ever compiled. I will also present new direct observations of Mg II host galaxies at z > 1 from the 3D-HST Survey. These analyses reveal compelling links between high equivalent width Mg II absorbers and large-scale star formation-driven outflows, which I will discuss in the context of other recent findings from the literature.